1. Field of the Invention
This invention relates generally to deployable flow control devices for flow surfaces and, more particularly, to deployable flow control devices for flow surfaces which are fast acting with throws sufficient to affect flow surface dynamics and robust enough to withstand the rigors of operating environments.
2. Description of Related Art
Military aircraft sometimes experience severe and drastic problems involving sudden and uncontrollable loss of aerodynamics during certain maneuvers, especially combat maneuvers. This loss of aerodynamics typically relates to two major factors, wing stall and forebody flow asymmetries. These two factors can occur when the flow surface is at high angles of attack, which happens during take-off and landing and during high speed maneuvers. This loss of aerodynamics compromises the effectiveness of the aircraft and can contribute to damage to the aircraft and injury or even death of the pilot. These experiences have been widely reported in the media and have gained world-wide attention.
As fluid flows over a flow surface, like air over an airplane wing or nose cone, air over turbine engine blades, or water around a ship or submarine, it forms a fluid boundary layer at the flow surface. The fluid boundary layer is a thin layer of viscous flow having laminar characteristics and exhibiting certain dynamics affecting the operation of the flow surface. A free stream of fluid flows above the fluid boundary layer. At a point along the flow surface the fluid boundary layer separates from the flow surface. In the case of a wing, if the separation is too near the leading edge, the wing stalls and the aircraft looses lift and the pilot looses control. In the case of the nose cone, flow separation occurs asymmetrically on the surface of the nose cone. Once asymmetric flow separation occurs, asymmetric vortices result and often generate large pressure differences across the nose which result in large side forces. These side forces decrease control and maneuverability.
Flow control devices have been employed to control fluid boundary layer dynamics and counteract the boundary layer separation point. These devices can be categorized as active or passive. Active devices, such as adjustable flaps and rudders, actually change the shape of the flow surface. Passive devices, such as vortex generators, tapered fins, scoops, flow-jet injectors and minidomes, protrude into or through the fluid boundary layer and enhance the mixing of the fluid on the flow surface and thereby, control fluid boundary layer dynamics.
Boundary layer separation occurs during certain situations of fluid flow. The presence of a device protruding from the flow surface when boundary layer separation is not occurring produces a drag on the flow surface resulting in increased fuel consumption and reduced efficiency of the craft. Also, with respect to military aircraft, protruding passive flow control devices can produce a radar signature compromising the stealth capability of the aircraft. Therefore, the device should be capable of being removed from the flow surface when not needed, especially in stealth required regimes.
Also, the dynamic benefit to be gained from the device must more than offset its overall weight and power requirements (including the weight and power requirements of its peripheral equipment) and should be retrofitable to flow surfaces of craft already in operation.
Accordingly, a need exists for a deployable flow control device to control fluid boundary layer dynamics that can be dependably and repeatedly deployed and retracted, be small and light weight have sufficient throw to affect the boundary layer flow for all operating conditions, and be robust enough to withstand the harsh environment on the flow surface. The device should also be economically retrofitable to craft already in operation.